This invention relates generally to printed images for mass produced articles, and more particularly to an absorbent article with a high quality ink jet image made on a fast moving substrate during assembly of the article.
Graphics are commonly printed on articles of manufacture to increase their aesthetic appeal. One example of this is graphics or images printed on absorbent garments, such as infant and children's diapers and training pants. The outer covers of these articles are nearly always imprinted with brightly colored images in the form of designs and characters that are pleasing to the child and caregiver. However, images may also be printed on other absorbent articles such as feminine healthcare products, adult incontinence garments and bandages. The article need not relate to personal care, and could be for example, a cleaning wipe.
Traditionally, imprinting the outer cover material, or a portion of the article with an image has been carried out by flexographic and rotogravure printing techniques prior to assembly of the absorbent garment. For example, outer cover material pre-printed with the image may be moved or shipped to the location where the absorbent garment is assembled and fed into the assembly apparatus. Certain inefficiencies arise from printing the images off line from the general assembly process through the shipping and handling of the outer cover material. However, printing the image in the manufacturing line has not been practical because it is difficult, time-consuming, and costly to change the printed image with traditional flexographic and rotogravure or other contact printing processes. The ability to change the image being printed is very limited and if a change is made, the entire assembly process must be shut down. Additionally, these types of printing processes create a significant amount of waste and delay during starting and stopping and other transitory process changes, and therefore do not lend themselves to the manufacture of mass produced articles.
Further, the types of materials that have utility in mass produced articles such as diapers, often have properties that can complicate flexographic or rotogravure printing. For example, the materials may be porous, thermally sensitive, stretchable/elastic, or unstable in the machine direction. Moreover, the materials may have low tensile properties, embossing or three dimensional topography, or surface tensions that are not compatible with inks (e.g., being hydrophobic or hydrophilic). Also these processes require contact to transfer the ink to the web, which often causes distorted, smeared, or unclear images.
Ink jet non-contact printing systems are known to provide flexibility in image printing. Change from one image to the next can be done rapidly, and even on the fly. Drop on demand piezoelectric ink jet printing apparatus have been used to apply inks to a variety of substrates. Generally, a drop on demand piezoelectric ink jet printing apparatus discharges small individual droplets of ink onto a substrate in a predetermined pattern. In this type of apparatus the printhead does not contact the web on which it prints. Such an apparatus typically incorporates a printhead having an array of orifices in a block, and a controller. The orifices are customarily arranged in a row in closely spaced relation. The printheads are controlled by the controller, which can be keyed by an operator to operate the printhead according to a programmed schedule to print one or a series of images.
Each orifice is designed to emit a single droplet of ink each time its associated printhead fires. The droplets, emitted according to the programmed sequence, are directed toward a substrate and form a dot. The image is built up from these dots. The quality of print produced by a drop on demand ink jet printer requires among other things, a certain area of coverage of the substrate by the ink. Thus, it is desirable for a greater surface area of the web to be covered by a given amount of applied ink, and for there to be a higher number of dots per unit area (i.e., dots per inch or “dpi”). However when the substrate is running under the orifices at high speed (e.g., 366 meters per minute (1,200 feet per minute) or greater), it is very difficult for the printhead to fire rapidly enough to put down a large number of dots per inch. This is particularly true where, as a result of the operation of the absorbent garment assembly apparatus, the image must be formed in a single pass of the material on which the images are formed under the ink jet printheads.
Heretofore, images formed at production line speeds by piezoelectric jet printers of the type described have been unsatisfactory. To achieve images of the necessary quality with ink jet printers, it has conventionally been necessary to use multiple passes of the printhead over the substrate and resolutions greater than 300 dpi. Among other problems, a substantial quantity of ink is used which drives up cost. Moreover as mentioned above, conventional ink jet printing processes have not been successful in producing commercially acceptable images where the substrate moves rapidly (e.g., 100 fpm and more) beneath the printheads. While there has been progress in the area of ink jet printing, the ink jet printers have been limited in that they were not able to produce an image of a commercially acceptable quality at the line speeds encountered in the assembly of an absorbent garment such as a diaper or training pant.